Aerosol canisters are widely used in domestic, commercial and industrial situations for the application of a range of chemicals. Typical examples of chemical products which are dispensable in this way include cosmetics, health products, paints, pharmaceuticals and agrochemicals. Frequently there is a need to attach mechanical or electrical devices to such aerosol canisters, for example to regulate or record the flow of chemical from the canister, or to act as environmental sensors. Such devices may be affixed to the canisters by a range of technologies including the use of adhesives and heat treatment, such as soldering or welding. However, the attachment of such devices to aerosol canisters poses difficulties in terms of producing a secure joint without affecting the integrity of the chemical by the application of excess heat during the heating or welding process. Similarly, the use of adhesives may lead to contamination problems due to the presence of low concentrations of volatiles from the adhesive on dispensing the chemical.
Medicament dispensers are extensively used in the administration of medicines, particularly those for the treatment of respiratory disorders. Medicaments which are contained in an aerosol and are administered to a patient by means of an inhalation device are widely used in such therapy. These inhalation devices typically comprise a tubular housing or sleeve in which the aerosol canister is located and an outlet tube leading from the housing. The aerosol canisters used in such inhalation devices are designed to deliver a predetermined dose of medicament upon actuation; the valves can be opened either by depression of the valve member itself or by depression of the canister while the valve member is held stationary. In the use of such devices, the aerosol canister is placed in the tubular housing with the outlet valve member of the canister communicating via a support with the outlet tube, for example a nozzle or mouthpiece.
A recent development in this field of technology is the use of mechanical or electrical dose counters to register the number of medicament doses used or remaining within the medicament dispenser. Dose counters can be positioned within the tubular housing and operate by means of detecting movement of the housing relative to the aerosol canister on actuation of the dispenser by the patient. The indexing mechanism of the dose counter registers the actuation of the dispenser and the counter displays how many doses have been used or remain within the aerosol canister.
Some dose counters are detachable from the aerosol dispenser. One disadvantage of such devices is that the individual components may become separated and used in isolation from each other. Another disadvantage of these devices is that once the dose counter is removed from the aerosol canister it may be tampered with, typically by young children, to give a false reading. Detachment of the dose counter from the aerosol canister could therefore result in false readings on re-attachment to the canister. Furthermore, with patients having several different inhalers, the indicating device could be re-attached to the wrong dispenser.
Other dose counters are essentially irreversibly attached to the aerosol dispenser. One means of affixing dose counters to aerosol canisters is to use a ‘snap-fit’ mechanism whereby a tubular grip assembly on the dose counter housing is pushed into position around the neck of the valve ferrule thereby locking the two components together. Whilst this arrangement holds the two structures securely together there can, on occasions, be some lateral movement or ‘play’ of one component relative to the other. As mechanical dose counters operate by registering relative movement of the aerosol canister to the dose counter housing, any play or lateral movement can result in false readings being registered on the dose counter. A key factor in the successful operation and functioning of such dose counters is that there be minimal movement of the housing relative to the aerosol canister out with the actuation cycle.
Dimensional variation resulting from manufacturing tolerances of aerosol canisters and dose counter housings poses additional problems in the assembly and operation of medicament dispensers. In order that the dose indicator mechanism functions correctly the canister and the counter housing must fit together tightly. Thus any variations in the dimensions of either of these components which result in a loose fit between the counter housing and the canister can lead to increased relative movement and the problems of false readings discussed above.
To overcome these problems of dimensional variation, stringent tolerance levels must be set for the manufacture of both the counter housing and the aerosol canister. This approach, together with the high levels of quality control necessary to ensure that both components meet the required engineering standards, is expensive for the manufacturer.
It is an object of the present invention to address the aforementioned problems associated with attachment of a mechanical or electrical device to an aerosol canister, in particular for the attachment of a dose counter housing thereto. The present invention involves joining the device housing to a ring or collar affixed around the neck of an aerosol canister to minimise the relative movement of the component parts. This joining can be achieved by a variety of technologies, including melting the components together by means of ‘hot staking’, soldering the surfaces together, or using adhesives to bind the housing to the collar. Welding technologies are particularly well suited for this purpose.